Toroid transformers and inductors are often used in switch mode power supplies due to their good magnetic performance. Such toroid magnetic devices are normally mounted using one of the following approaches:                Mechanical bolting to part of the power supply structure and connection using flying leads.        Mechanical bolting to a PCB (printed circuit board) with lead-out connections made by hand.        Bonding to a through-hole mounting plate and soldering into a PCB.        Bonding to a surface-mount mounting plate and re-flow soldering to a PCB        
Regardless of the mounting approach, the device temperature rise can be taken to be a function of surface area, one standard equation being:Temperature Rise (° C.)=[Power Dissipation (mW)/Surface Area (cm2)]0.833 
FIG. 1 shows a graph plotting temperature rise against power dissipation for five toroid transformers having different surface areas, with the Table below the graph providing approximate core diameters and heights for the five surface areas plotted (assuming approximately 40% winding factors). In many commercial applications these relatively high temperature rises are tolerable. However, in harsh environment, safety critical applications, such as aerospace engine controls, the allowable temperature rise may be limited to 35° C. in order to achieve required component life. Also, in order to achieve adequate thermal performance in higher temperature applications, the power dissipation of a toroid transformer (or inductor) may be limited to <2.5 W unless a large geometry core can be used.
With the increased desire for automated assembly, surface mount applications are becoming more common. However, in harsh environment applications with high vibration requirements (such as aerospace engines) the mass of surface mount components should be minimised, which is in direct contradiction to the need to increase the size of the component for improved thermal performance.
There is therefore a need for improved thermal management of surface mount toroid magnetic devices to enable use in safety critical, high temperature, harsh environment applications.